The present invention relates to a fuel injection control apparatus of a cylinder injection type internal combustion engine.
For example, Japanese Laid-Open Patent Publication No. 10-18884 discloses a fuel injection control apparatus that includes main fuel injection valves, each of which directly injects fuel into one of the combustion chambers (cylinders), and an auxiliary fuel injection valve, which injects fuel into an intake passage. In the case with the fuel injection control apparatus of the publication, part of fuel required for cranking the engine is injected from the auxiliary fuel injection valve, in addition to the fuel injected from main fuel injection valves. Injected fuel is sufficiently mixed with intake air flowing through the intake passage and is introduced into the corresponding combustion chamber after being vaporized. Since the auxiliary fuel injection valve also injects fuel, the engine is reliably started.
In the above mentioned internal combustion engine, fuel that is highly pressurized by a high pressure pump, which is driven by the engine, is supplied to each main fuel injection valve to inject the fuel from each main fuel injection valve against the pressure in the corresponding combustion chamber.
During cranking of the engine and immediately after the engine is started, fuel is not pressurized sufficiently by the high pressure pump. Therefore, the pressure of fuel supplied to each main fuel injection valve is low and atomization of fuel injected from the main fuel injection valve is insufficient. In addition, when the fuel pressure is decreased, the amount of fuel injected from each main fuel injection valve per unit time is decreased. Thus, the fuel injection time needs to be increased to inject an amount of fuel that is the same as the amount of fuel that is injected when the fuel pressure is not decreased. When the fuel injection start timing is advanced to the top dead center or in the vicinity of the top dead center of the intake stroke of each piston, fuel is injected when the piston approaches the corresponding main fuel injection valve. Thus, the fuel adheres to the top surface of each piston. When the engine is started, the temperature of the top surface of each piston is low and the adhered fuel is not easily vaporized. Therefore, the amount of fuel adhered to the top surface of each piston gradually increases and the fuel is accumulated in the form of liquid. The fuel adhered to the top surface of each piston causes incomplete combustion. Accordingly, black smoke is exhausted, which deteriorates emission during the cranking of the engine.
A few measures have been introduced to address the above draw back. For example, Japanese Laid-Open Patent Publication No. 11-270385 discloses a fuel injection control apparatus that starts fuel injection from a main fuel injection valve on condition that the fuel pressure becomes greater than or equal to a predetermined value. According to this fuel injection control apparatus, atomization of fuel is prevented from deteriorating, and the amount of fuel that adheres to the top surface of each piston is decreased, which suppresses emission of black smoke.
Since only small amount of fuel contributes to combustion at a very low temperature, a large amount of fuel is required particularly during the cranking of the engine. In this state, the amount of fuel injected from the fuel injection valves becomes greater than the amount of fuel discharged from the high pressure pump. This decreases the fuel pressure after the fuel injection is started.
When the auxiliary fuel injection valve is located in the intake passage, the required amount of fuel is injected from the auxiliary fuel injection valve. Thus, the amount of fuel injected from each main fuel injection valve can be reduced to suppress the decrease of the fuel pressure. However, it takes a predetermined time for the fuel injected from the auxiliary fuel injection valve to flow into the combustion chambers. In the meantime, a large amount of fuel needs to be injected from each main fuel injection valve. Therefore, fuel pressure is greatly decreased during the time the fuel injected from the auxiliary fuel injection valve flows into the combustion chambers. This hinders sufficient suppression of the deterioration of the emission.
Accordingly, it is an objective of the present invention to provide a fuel injection control apparatus of a cylinder injection type internal combustion engine that suppresses deterioration of emission.
To achieve the above objective, the present invention provides a fuel injection control apparatus for an internal combustion engine. The internal combustion engine includes a cylinder, an intake passage, which is connected to the cylinder, a main fuel injection valve, and an auxiliary fuel injection valve. The main fuel injection valve directly injects pressurized fuel, which is supplied from a high pressure pump, to the cylinder. The auxiliary fuel injection valve injects fuel to the intake passage. The apparatus includes a controller. The controller controls the main fuel injection valve and the auxiliary fuel injection valve. The controller causes the auxiliary fuel injection valve to inject fuel during the cranking the internal combustion engine and determines whether the pressure of the pressurized fuel is greater than or equal to a predetermined value. The controller predicts whether the pressure of the pressurized fuel decreases below a permissible value, which is less than the predetermined value, due to injection of pressurized fuel by the main fuel injection valve during a period from a point of time after the pressure of the pressurized fuel becomes greater than or equal to the predetermined value till when fuel injected from the auxiliary fuel injection valve reaches the interior of the cylinder through the intake passage. When the pressure of the pressurized fuel is greater than or equal to the predetermined value, and it is predicted that the pressure of the pressurized fuel will not decrease below the permissible value during the period, the controller causes the main fuel injection valve to start injecting the pressurized fuel.
The present invention also provides a controlling method of a fuel injection control apparatus of an internal combustion engine. The internal combustion engine includes a cylinder, an intake passage, which is connected to the cylinder, a main fuel injection valve, and an auxiliary fuel injection valve. The main fuel injection valve directly injects pressurized fuel, which is supplied from a high pressure pump, to the cylinder. The auxiliary fuel injection valve injects fuel to the intake passage. The method includes: causing the auxiliary fuel injection valve to inject fuel during cranking the internal combustion engine; determining whether the pressure of the pressurized fuel is greater than or equal to a predetermined value; predicting whether the pressure of the pressurized fuel decreases below a permissible value, which is less than the predetermined value, due to injection of pressurized fuel by the main fuel injection valve during a period from a point of time after the pressure of the pressurized fuel becomes greater than or equal to the predetermined value till when fuel injected from the auxiliary fuel injection valve reaches the interior of the cylinder through the intake passage; and causing the main fuel injection valve to start injecting the pressurized fuel when the pressure of the pressurized fuel is greater than or equal to the predetermined value, and it is predicted that the pressure of the pressurized fuel will not decrease below the permissible value during the period.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.